SUbstance flow analysis of the recycling of small waste electrical ...

30 Substance flow analysis of the recycling of small WEEE
The extraction of precious metals through mining is associated with significant environmental
impacts like emissions of greenhouse gases, and consumption of energy, water and land
(Ayres 1997). According to the Wuppertal Institute (2003), gold has a material intensity (MIT)
of 540 000, which means that 540 tonnes of material have to be used to produce one gram
of gold (Ritthoff et al. 2002). The MIT of silver is 7 500 (Wuppertal Institute 2003). Palladium
has a MIT of 99 891 (primary production) or 2 394 (secondary production) (Saurat &
Bringezu 2008). For comparison, primary copper has a MIT of 348.47 and secondary copper
of 2.38 (Wuppertal Institute 2003). The environmental impacts of the secondary production of
precious metals in state-of-the-art operations are much lower than primary production
(Hagelüken & Meskers 2008). According to Saurat & Bringezu (2008), carbon dioxide
equivalent emissions associated with secondary production of platinum-group metals in
Europe are lower by a factor 13 than primary production outside of Europe, and sulphur
dioxide equivalent emissions are lower by a factor 107.
2.3.2. Use of precious metals for manufacturing EEE
Around 12% of the primary production of gold, 30% of the primary production of silver and
15% of the the primary production of palladium were used in 2006 for manufacturing EEE
(Hagelüken & Meskers 2008). Precious metals are used in printed circuit boards (PCB) as a
component of complex material mixtures, as they are mixed with or connected to other
metals in contacts, connectors, cables, solders, hard disk drives, etc., with ceramics in multi
layer capacitors, integrated circuits, hybrid ceramics, etc. or with plastics in PCB-tracks,
interboard layers, integrated circuits, etc. (Hagelüken 2006a).
The great advantage of gold is its high resistance to oxidation and corrosion and its high
conductivity (Renner et al. 2000). Gold and gold alloys are used for conductor material and
low-voltage contacts for communication and information transfer equipment, where even very
thin oxide layers would cause interruptions or failures in signal transfer (Renner et al. 2000).
Silver, due to its high electrical and thermal conductivity, is used as conductor and electrode
material (Brumby et al. 2008). Palladium, pure or in combination with silver, is the most
important component in pastes used for the production of inner electrodes of multilayer
capacitors. Palladium is also used as a component in silver-based conductor pastes and for
resistor elements in thick-film circuitry. Platinum finds application for data storage in harddisk
drives, as barrier layers and as contact pads on semiconductor chips (Hagelüken & Meskers
2008, Renner et al. 2001). Table 3 gives a survey of the main application fields of gold,
silver, palladium, platinum and their alloys.